User`s manual

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25
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(IFM), compressor no. 1, and condenser fan start. The outdoor
(condenser) fan motors (OFM) run continuously while unit is
cooling. If the thermostat calls for a second stage of cooling by
energizing Y2, compressor con-tactor no. 2 (C2) is energized
and compressor no. 2 starts. When the thermostat is satisfied,
C1 and C2 are deenergized and the compressor and OFM shut
off. After a 30-second delay, the IFM shuts off. If the thermo-
stat fan selector switch is in the ON position, the IFM will run
continuously.
With Durablade Economizer
When the outdoor-air temperature is above the OAT (outdoor-
air thermostat) setting and the room thermostat calls for cool-
ing, compressor contactor no. 1 is energized to start compres-
sor no. 1 and outdoor fan contactor (OFC) energizes starting
the condenser fan. The evaporator-fan motor is energized and
the economizer damper moves to the minimum position. After
the thermostat is satisfied, there is a 30-second delay before
the evaporator fan turns off. Upon a further call for cooling,
compressor contactor no. 2 will be energized, starting com-
pressor no. 2. After the thermostat is satisfied, the damper
moves to the fully closed position when using an auto. fan or
to the minimum position when using a continuous fan.
When the outdoor-air temperature is below the OAT setting and
the thermostat calls for cooling, the economizer dampers move
to the minimum position. If the supply-air temperature is above
57 F, contact T2 on the supply-air thermostat (SAT) will close.
The damper continues to open until it reaches the fully open
position or until the supply-air temperature drops below 52 F.
When the supply-air temperature falls to between 57 F and
52 F, contactor T2 and T1 on the SAT will open and the
damper will remain at an intermediate open position. If the
supply-air temperature falls below 52 F, contactor T1 on the
SAT will close. The damper will modulate closed until it
reaches the minimum position or until the supply-air temper-
ature is above 52 F. When the thermostat is satisfied, the
damper will move to the fully closed position when using an
auto. fan or to the minimum position when using a continuous
fan.
If the outdoor air alone cannot satisfy the cooling requirements
of the conditioned space, economizer cooling is integrated with
mechanical cooling, providing a second-stage cooling. Compres-
sor no. 1 and the condenser fan will be energized and the posi-
tion of the economizer damper will be determined by the
supply-air temperature. Compressor no. 2 is locked out.
When the second stage of cooling is satisfied, the compressor
and condenser-fan motor will be deenergized. The damper
position will be determined by the supply-air temperature.
When the first stage of cooling is satisfied, there is a
30-second delay before the evaporator fan shuts off. The
damper moves to the fully closed position when using an
auto. fan or the minimum position when using a continuous
fan.
Additional information on economizer operation is provided
in the Ventilation Sequence section on page 31.
Cooling, Units with EconoMi$er
When the Outdoor Air Temperature (OAT) is above the
ECON SP set point and the room thermostat calls for
Stage 1 cooling (R to G + Y1), the indoor-fan motor (IFM) is
energized and the EconoMi$er damper modulates to mini-
mum position. The compressor contactor OFC are energized
to start the compressor and outdoor-fan motor (OFM). After
the thermostat is satisfied, the damper modulates to the
fully closed position when the IFM is deenergized.
When the OAT is below the ECON SP setting and the room
thermostat calls for Stage 1 cooling (R to G + Y1), the
EconoMi$er modulates to the minimum position when the
IFM is energized. The EconoMi$er provides Stage 1 of cooling
by modulating the return and outdoor-air dampers to main-
tain a 55 F supply air set point. If the supply-air temperature
(SAT) is greater than 57 F, the EconoMi$er modulates open,
allowing a greater amount of outdoor air to enter the unit. If
the SAT drops below 53 F, the outdoor-air damper modulates
closed to reduce the amount of outdoor air. When the SAT is
between 53 and 57 F, the EconoMi$er maintains its position.
If outdoor air alone cannot satisfy the cooling requirements
of the conditioned space, and the OAT is above the MECH
CLG LOCKOUT set point, the EconoMi$er integrates free
cooling with mechanical cooling. This is accomplished by the
strategies below.
NOTE: Compressors have a two-minute Minimum On, Mini-
mum Off, and Interstage delay timer.
1. If Y1 is energized, and the room thermostat calls for
Y2 (2-stage thermostat), the compressor number 1
and OFM are energized. The position of the
EconoMi$er damper is maintained at its current
value.
2. If Y1 is energized for more then 20 minutes, and Y2 is
not energized (whether or not a 2-stage thermostat is
used), compressor no. 1 and OFM are energized. The
position of the EconoMi$er damper is maintained at
its current value.
3. If Y1 is energized, and compressor no. 1 is already
energized (see Step 2) and the room thermostat calls
for Y2, compressor no. 1 continues to operate. If Y2
remains energized for more than 20 minutes, com-
pressor no. 2 is energized.
NOTE: Compressor no. 2 cannot be energized unless there is
a signal for Y2 from the space thermostat.
4. If compressor no. 2 is energized, and the Y2 signal
from the thermostat is satisfied, compressor no. 1 and
2 are deenergized. Re-asserting Y2 will start com-
pressor no. 1 and (after a 20-minute interstage delay)
compressor no. 2.
5. If compressor no. 1 is energized and the thermostat is
satisfied, compressor no. 1, the OFM, and IFM are
deenergized and the EconoMi$er modulates closed.
When the OAT is below the MECH CLG LOCKOUT set
point, the compressors remain off.
Time Guard
®
II Device
If the unit is equipped with accessory Time Guard II recycle
timer, the unit will delay 5 minutes between compressor
starts.
Controls Kit
Loss-of-Charge Switch (LPS) — When the refrigerant liquid
line pressure drops below 7 psig, the LPS opens 24-v power to
the compressor contactor and stops the compressor. When the
pressure reaches 22 psig, the switch resets and the compres-
sor is allowed to come back on.
High-Pressure Switch (HPS) — When the refrigerant high-
side pressure reaches 428 psig, the HPS opens 24-v power to
the compressor contactor and stops the compressor. When
the pressure drops to 320 psig, the switch resets and the
compressor is allowed to restart.
Freeze Protection Thermostat (FPT) — When the evaporator
coil leaving-refrigerant temperature drops below 30 F, the
FPT opens 24-v power to the compressor contactor and stops
the compressor. When the leaving refrigerant temperature
warms to 45 F, the switch resets and the compressor is
allowed to restart.